No direct postings can be made to G/L acct.** in CoCode **

hi all,
now i hava a material ,it is trading goods,it is used for create a third party trading SO.In our sap system,the SO is automatic generate PR when it is released,but now there is a wrong G/L Account No. with this PR, it lead that it shows a error when create PO with this PR,this error message:"No direct postings can be made to G/L acct. 1243201000 in CoCode *****".
I had check valuation class:3100 in the material master data, and check item category of PR is S and account assignment category is X, these are not different from other trading goods which can generate right G/L account No.successfully,so now i don't how to continue to check what it is wrong,pls consultants give me some advices , thanks in advance.
best regards

hi Murali,
In T-code:FS00, the Automatic Posting box is checked. Because this material is trading goods, it is purchased,it doesn't create MRP view in material master data,but now it created MRP view,if it didn't create MRP view,and it didn't have this error message in creating PO,after creating MRP view in material master data,it catch this error.i though which filed can lead this accout assignment in the MRP view.for example,stratery group and so on,because i try to clear the stratery group field ,it didn't catch the error message when creating with this PR.